Bill,
I don't know whether this will answer your question. I think AutoCAD/ADT installation on XP is flawed in process. If one installs AutoCAD in the same account as they are using it, then the files are not set up correctly. If I had to do it again, I would create a non-functional administrator account.
The plotstamp file that is current on your system is marked read-only. To change that, search for *.pss on your system and uncheck the read-only option.
There is a plotstamp command and a -plotstamp command.
The -plotstamp command is a bit more informative.
Personally, I love the plot.log files.